Pressure sensitive adhesive (PSA) sheets, films, and tapes are often difficult to apply to a substrate at a precise location without air entrapment or wrinkles, primarily due to preadhesion or "quick stick" behavior of the PSA. This is particularly true for "aggressive" PSAs that have high bond strengths and/or low temperature tack properties, and is especially problematic as the size of the article increases. Several methods and configurations have been developed to make the application of PSA films and tapes easier.
For example, application aids, such as formulations containing a surfactant, water, and alcohol, or dry application aids containing particles, powders, or talcs, have been used to eliminate preadhesion. Such application aids, however, tend to affect the adhesive properties of the PSA and prevent rapid formation of a strong bond between adhesive and substrate.
Discontinuous coatings of nontacky materials projecting from the adhesive surface have also been used to prevent preadhesion of the PSA during application. Articles with these coatings can be placed against a substrate and freely moved over the substrate. Such coatings include patterned polymer coatings, particles, and films, for example. Yet another configuration used to make PSA films and tapes easier to apply uses a random distribution of hollow glass microspheres partially embedded in the adhesive as a means to prevent contact and preadhesion. Pressure application crushes the microspheres, permitting the adhesive to contact the substrate and form a strong bond instantly.
Other methods of dealing with preadhesion include formation of pegs of adhesive, optionally containing beads, protruding from the PSA surface. Topographically structured adhesives have also been described. Various adhesive layer topographies include concave and convex V-grooves or hemispheres, and other three dimensional shapes. In general, these topographies provide adhesive sheets, films, and tapes with lower peel adhesion values in comparison with smooth-surfaced adhesives. In many cases, the topographically-structured adhesives also display a change in adhesion with increasing contact time.
These adhesive articles exhibit various types of positionable and repositionable behavior. Certain of these articles can suffer from problems, however. Therefore, alternative adhesive articles are needed for avoiding preadhesion when using pressure sensitive adhesives.
Furthermore, it is desirable that articles be removable from substrate surfaces on demand without damaging the substrate. Release on demand has been addressed using microsphere adhesives and tapes that release upon mechanical stretching. In spite of these approaches, however, there is a continuing need for articles which exhibit both ease of application and ease of removal.